1. Field of the Invention
The present invention relates to a radio communication apparatus for establishing a radio telecommunications network, and also to a method for reestablishing a radio telecommunications network of a radio communication apparatus.
2. Description of the Background Art
A radio communication system for establishing a radio telecommunications network, such as a multi-hop network, may be formed into a tree structure as its network topology, i.e. tree topology. The tree topology is more advantageous over the other types of network topology, e.g. in simplicity of the management of routing information.
By way of example of a radio communication system employing the tree structure for network topology, there is ZigBee (trademark of Koninklijke Philips Electronics N.V.) network system, which is disclosed by, for example, “ZigBee Specification”, Document 053474r13, ZigBee Alliance, pp. 323-352, according to which a radio communications device, or node, when going to join the network, sends out a signal to join the network to the nodes that form the network so as to start joining the network.
Reference will be made first to FIG. 1 for further describing a conventional network reestablishing operation for better understanding the present invention. FIG. 1 is a schematic block diagram showing a tree topology network 100, which comprises a base station 102, nodes 1000-1121 denoting radio communications devices and links 110 between the nodes 1000-1121 denoting routings. The nodes 1000-1121 constitute a hierarchical or layered tree structure where the node 1000 is a root node thereof, and in one level lower than the node 1000 is the node 1100, which resides in a higher layer, or level, in the hierarchy than the nodes 1110 and 1120 and in the same layer as the node 1200.
In such a tree topology network, if the node 1000 serving as the root node becomes inoperable so that the remaining nodes 1100-1121 have to be disengaged from the network all at once, then those nodes simultaneously send out signals for participating in the network, so-called join signals, which will in turn cause numerous collisions, thereby taking so much time to reestablish the network. Furthermore, the establishment of a tree structure depends on the timing at which join signals are transmitted. Therefore, if all nodes send out the join signals simultaneously, the network reestablished may significantly differ in tree structure before reestablished. By way of example, after reestablished, the node 1200 could be in a lower layer than the node 1100.
In a network having its tree structure established on the basis of the physical positional relationship of the nodes, the problems become more pronounced if higher nodes become inoperative.